1. Technical Field
The present disclosure relates to a conductive ball removing method, a conductive ball mounting method, a conductive ball removing apparatus, and a conductive ball mounting apparatus. More particularly, according to the present disclosure, conductive balls are mounted on a semiconductor substrate (such as a wiring substrate or a silicon wafer) having a plurality of pads thereon through a mask having a plurality of through holes and then remaining conductive balls that have not been directly mounted on the pads are removed.
2. Background Art
In mounting a semiconductor device such as Large Scale Integration (LSI), Liquid Crystal Display (LCD), or the like on a mounting substrate by flip-chip bonding, electric connections are provided by putting micro particles made of conductive metal between electrode pads of a semiconductor device and electrode pads of the mounting substrate and then applying thermo-compression bonding to the micro particles. As the micro particle, a conductive ball such as a solder ball is used.
In order to achieve the electric connection between the pads by using such conductive ball, prior to the thermocompression bonding, each of the conductive balls must be mounted on corresponding one of all pads designed to be aligned. Therefore, in order to mount each of the conductive balls on corresponding one of the pads as aligned, there is known a method of dropping a sufficient number of conductive balls onto the pads through a mask having the same alignment as the pads.
Such a method of dropping the conductive balls through the mask is a simple method, but surplus conductive balls are put inevitably on the mask. FIG. 1 shows a state that the surplus conductive balls are mounted on the mask. As a result of dropping conductive balls 38 through a mask 12 to mount each of the conductive balls 38 on corresponding one of the pads 27 formed on an upper surface of a wiring substrate 18, some conductive balls are put on the mask 12 and other conductive balls are put on the conductive balls being directly mounted on each pad 27.
Therefore, surplus conductive balls need to be removed on the mask after the mounting operation before removing the mask. This is because, if the mask is removed in such a condition that the removal of the surplus conductive balls is still insufficient, two conductive balls are stacked on the pad 27 (double balls), which leads to a failure of short-circuit between the pads. A situation that the double balls occur after the mask is removed is shown in FIG. 2.
As the method of removing such surplus conductive balls, there are a method using a brush and a method using an air blow.
According to the method using the brush, the conductive balls are removed by moving the conductive balls with the brush. For example, JP-A-9-148332 describes the method of moving the conductive balls using the brush-like squeegee on which electrically conductive fibers are implanted. Also, JP-A-2006-19741 describes an example of the method of moving the conductive balls using the squeegee on which a plurality of sweeping members are aligned in a multiple fashion. Further, JP-A-2006-173195 describes an example of the method of moving the conductive balls by bringing fiber sweeping members into contact with a surface of the mask and then moving the sweeping members while deforming them.
According to the method using an air blow, the conductive balls are moved by using an air jet from the air blow as a driving force. For example, JP-A-2006-19741 describes an example of the method of moving the conductive balls by using the head equipped with air nozzles. Also, JP-A-2006-173195 describes an example of the method of moving the conductive balls by using a removing head, in which the conductive balls are blown away by blowing an air obliquely downward toward the mask.
However, in the conductive ball removing method in the related art, the following disadvantages existed.
In the method of using the brush, when the brush is used continuously, the conductive balls enter into the brush and thus the removal cannot be completely achieved. Also, when the brush is used continuously, the conductive balls enter into the implanted fibers and do not come out of the implanted fibers, and thus the subsequent removal of the conductive balls becomes difficult. Also, sometimes the conductive balls that have entered into the implanted fibers once drop on the area where the removal has already been completed, and thus the reliable removal becomes difficult.
Further, in the method of using the air blow, the conductive balls are scattered by the air. When the conductive balls are scattered, sometimes such balls are returned to the area where the removal has already been completed, and thus the reliable removal becomes difficult.